1. The Field of the Invention
The present invention relates to a process of bioremediation for contaminated earth and solid waste, herein referred to as permeable xe2x80x9cmediaxe2x80x9d. More specifically, the present invention relates to a process of applying an emulsion containing an electron donor material to contaminated media to facilitate long-term anaerobic conditions for reducing harmful contaminants in the media to less harmful or insoluble material.
2. The Relevant Technology
Many industries, including mines, fossil fuel power plants, pulp and paper mills, chemical processing plants, oil refineries and phosphate fertilizer manufacturers create byproducts or waste that may contain environmentally harmful materials. These byproducts and waste materials are typically stored in waste sites that take the form of land fills, tailings piles, dumping grounds, spent ore heaps, sludge ponds, and the like. They can contaminate their surrounding environment adversely affecting the adjacent earth, surface water, subsurface ground water, and other media with which the contaminated media comes into contact. Additionally, meteoric water can cause certain contaminants to leach out of the contaminated media. Acid rock drainage is an example of a contaminated leachate.
Metal sulfates and sulfuric acid are constituents of acid rock drainage from tailings piles and the like. When in the earth, pyrite, other minerals and selenium are not susceptible to oxygen and aerobic conditions which may transform the solid sulfides, selenium, or other compounds into more dangerous soluble sulfates, selenates, and the like. However, once mined and brought to the surface, tailings piles and waste from mining and processing facilities etc., become susceptible to oxygen by exposure to air or rain. This creates the aerobic conditions which allow sulfide, selenium and other insoluble materials to transform into soluble sulfates and selenates. These soluble materials can leach out of the media in which they reside and may pose a problem to groundwater or the surrounding environment. This is especially true given the large quantities of waste rock and tailings in many mining operations.
Bioremediation is increasingly being used to destroy contaminants such as hazardous organic compounds, cyanide, and other potentially harmful byproducts of industrial processes. Many bioremediation processes require that contaminated water be pumped from the ground and treated by passage through bioreactor tanks. The problem with these processes is that the removal step is costly, requiring extra equipment and space for treatment facilities.
In situ bioremediation has been used to overcome some of the higher costs of offsite treatment. In situ bioremediation involves enhancing the activity of an indigenous bacteria consortium in order to accelerate a decontamination process at the site being treated. The enhancement is often accomplished by optimizing the availability of needed nutrients. This allows the bacteria consortium to facilitate conditions in which contaminants are transformed chemically or biochemically and rendered harmless in place, without requiring costly pumping, or other means of removal, or further processing of effluents above ground.
Bacteria derive their energy from oxidation-reduction reactions. In the absence of oxygen, anaerobic respiration can occur if other molecular species are present to provide oxygen or accept electrons. Soluble ferric, nitrate, carbonate, and sulfate ions have been used to provide oxygen or accept electrons.
The electron donor nutrient or material often used for in situ anaerobic bioremediation may be a form of organic carbon. Two common material forms of organic carbon are known in the art: (1) solid or semi-solid biomass and (2) soluble aqueous solutions which may include carbohydrates, organic acids, and/or organic salts. Both of these, however, suffer drawbacks. Solid biomass is difficult to introduce and disseminate within the media being treated. Aqueous solutions containing soluble materials are easily introduced by gravity infiltration or injection wells, but are leached out leaving no permanent protection against the reintroduction of oxygen into the media.
With respect to solid sources of carbon, U.S. Pat. No. 4,990,031 (Blowes et al.) teaches the treatment of mine tailings with a layer of biomass placed in the tailings impoundment below the elevation of the final saturated water level in it. Biomass (e.g. wood chips) can also be introduced with the tailings slurry stream entering the impoundment. U.S. Pat. Nos. 5,362,394 and 5,514,279 also by Blowes et al. teach the use of a reactive wall of porous material containing disseminated biomass to intercept and treat groundwater from a tailings impoundment. U.S. Pat. Nos. 4,519,912 and 4,522,723 (Kauffman et al.) treat wastewater, including mine wastewater, flowing through a treatment zone (reactive wall) consisting of a porous matrix containing nutrient and sulfate reducing bacteria.
However, direct injection of the bioremediation materials as slurries will result in the suspended solids occluding interstices of the media preventing, or at least making difficult, further flow. This is impractical, and commercial application would be costly and difficult. Furthermore, solid organic materials, such as those used in prior art applications, tend to seal the media interstices. Because of pore plugging, they cannot be used for surface infiltration into contaminated media. With the possible exception of colloids, solids are also unsuitable for treating groundwater plumes.
Solid sources of carbon, sewage, wood chips, and biomass have been used to treat sulfate waste water. U.S. Pat. No. 5,738,789 (Shugina) teaches metal immobilization in groundwater plumes using an injection of sulfate reducing bacteria cultures derived from natural materials such as organic containing clay, sawdust, and vegetable remnants, which are solid or semi-solid materials. However, solids are not suitable for in situ treatment of media such as ground, soil, tailings in piles, mine waste, etc. because it is difficult, if not impossible to disseminate solids into the media.
Some attempts to overcome the solid bioremediation source material problem include providing water soluble sources of carbon in aqueous solutions. For example, U.S. Pat. No. 5,833,855 (Saunders) teaches bioremediation of groundwater using sulfate reducing bacteria and a soluble source of carbon nutrient, preferably sodium lactate. U.S. Pat. Nos. 5,554,920 and 6,143,177 (Suthersan) precipitate heavy metals with sulfate reducing bacteria, using wells to inject carbohydrate solutions (and sulfate if needed) into a saturated zone of the media. Metal immobilization by sulfate reducing bacteria using a liquid base containing an appropriate nutrient supplement is taught by U.S. Pat. No. 5,632,715 (Harrington et al.). This patent mentions water soluble carbohydrates including molasses, hydrolyzed potato starch, and milk whey. U.S. Pat. No. 5,710,361 (Harrington et al.) extends the claims from industrial wastes to earth materials.
Although carbohydrate nutrient solutions work well for metal immobilization and destruction of already dissolved contaminants, these nutrients are readily leached out of the media by continued flow of recycled solutions, groundwater and infiltrating meteoric surface water. Accordingly, soluble bioremediation material is not available to provide an effective long term solution. Moreover, soluble carbohydrates are relatively expensive.
Thus, it would be an advancement in the art to provide a more permanent environmental protection process using a bioremediation material that can easily enter the permeable contaminated media without clogging the media. It would be a further advancement to provide such a process that would provide long term retention and bioremediating conditions in the media. It would be yet another advancement to provide such a process using low cost bioremediation material. Such a bioremediation process is described and claimed herein.
The process of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available bioremediation processes. Thus, it is an overall objective of the present invention to provide a bioremediation process which facilitates decontamination by creating anaerobic conditions in a contaminated media using a permanent source of electron donor material to create lasting anaerobic conditions within the contaminated media. It is another objective of the present invention to provide a way to disseminate the electron donor material within the media without clogging the interstices within the media.
The bioremediation process of the present invention is in situ, or xe2x80x9cat the sitexe2x80x9d of the contaminated media. The contaminated media may include soil, earth, surface mining waste, underground mining wastes, mill tailings, spent ore heaps, industrial waste, sludge ponds, landfills, and the like. The process includes creating an emulsion of a water insoluble organic liquid phase and an aqueous liquid phase. The organic phase should be capable of donating an electron in a chemical or biochemical reaction. In one embodiment, the organic phase may be oil, derived from mineral or vegetable sources. In another embodiment, the organic phase may be a petroleum product or blend of petroleum products such as residual fuel oil and asphalt.
The organic phase may be present in the emulsion in an amount between about one-tenth of one percent (0.1%) and about eighty percent (80%) of the volume of the emulsion. In another embodiment, the emulsion may contain biological nutrients such as phosphate, nitrogen, and/or water soluble organic materials including carbohydrates. The emulsion provides a vehicle for insertion of the organic phase or material into the media without clogging it. The continuous or external phase of the emulsion is water or an aqueous solution that provides the desired surface tension and capillary action for the emulsion to infiltrate the media, wet its internal surfaces and penetrate its smaller pores. This leaves the nonwetting organic phase as droplets, well disseminated within the media, after emulsion breakage.
Microorganisms may be present in the media or added to the media with the aqueous phase of the emulsion. The microbes may be in sufficient proximity to the organic material to promote a reaction between the organic material and the media contaminant. In one embodiment, the microbe facilitates the reduction of sulfate contaminants to soluble H2 S or sulfide under anaerobic conditions. The microbes help precipitate metal contaminants such as As, Sb, Cd, Hg, Cu, Ni, Zn, Co, Mn, Ag, and Fe as metal sulfides. They may also help to alter the chemical composition of water soluble inorganic contaminants such as CNxe2x88x92, NO3xe2x88x92, NO2xe2x88x92, SeO42xe2x88x92, Cr6+, or UO22+ to create less harmful contaminants.
The organic/water emulsion may be applied to the media by distributing it on the surface of the media and allowing it to infiltrate or percolate into the media. In another embodiment, the emulsion may be inserted in the media by flowing into an injection well or other passage within the media. The emulsion may also be inserted into the media to form a reactive wall to intercept and treat a contaminant in water flowing through the media.
Once within the media, the emulsion may disengage (break) leaving the organic material retained as dispersed droplets within the media and adhering to internal media surfaces. Hence, it will not leach out, or be transported out, of the contaminated media by rain or other surface water. Thus, the organic electron donor material will be available to sustain anaerobic conditions within the contaminated media over a very long time to facilitate the chemical or biochemical reduction of harmful, soluble, contaminants to non-hazardous or insoluble forms.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.